Photoluminescence (PL) of chemically vapor deposited Si on silica aerogels has been investigated as a function of annealing temperature up to 650°C in air. The PL peak red shifts considerably with temperatures up to 350°C and then slightly blue shifts above 350°C. There are at least two different oxidation stages in the thermal annealing of porous Si: surface oxidation below 350°C, which results in higher luminescence yield particularly for large Si particles, and internal oxidation above 350°C, which reduces the effective particle size.